Hardenable steels



Patented Aug. 14, 1945 HARDENABLE STEELS Walter Crafts, Niagara Falls, N. Y., assignor to Electro Metallurgical Company, a corporation of West Virginia No Drawing. Application March 11, 1941, Serial No. 382,737. In Great Britain March 15, 1940 2 Claims.

This invention relates to steels, and more specifically to steels the hardness of which may be increased by rapid cooling from temperatures within or above the critical range. For the sake of simplicity of presentation, the application of the invention will be described herein principally as it may be applied to carbon steels containing 0.1% to 1% carbon, up to about 2% manganese, and between 0.25% and 2% silicon; but as the description proceeds it will be evident that the invention may be applied to a wide variety of hardenable steels.

When hardening steels by rapid cooling from high temperatures, it is often desired to .produce a deep or thick zone of hardened material rather than a thin or shallow hardened case.- The depth to which a piece of steel will harden, at a given rate of heat extraction, is different in different steels. The property of the steel which involves this relative susceptibility to mass effect in hardening seems to be inherent, and for convenience it will be termed herein deep-hardenability.

An accepted, convenient measure of deep-hardenability is afforded by the Jominy test, described in detail in A Hardenability Test for Carburizing Steel by W. E. Jominy and A. L. Boegehold, Trans. Am. Soc. for Metals, vol. 26, p. 574 (1938). To summarize briefly, the test is made on a small bar of steel of standardized shape and dimensions, and comprises heating the entire bar to the desired hardening temperature, quickly extracting heat through one end face of the bar, grinding oiT superficial scale and decarburized skin and producing a flat surface suitable for making a hardness test, and measuring the Rockwell C hardness along the length of the bar. As a means for readily expressing the relation between the hardness and distance from the hardened end, the distance from the hardened end at which the hardness becomes less than Rockwell C 50 is used and is referred to herein as the Jominy depth. If the same hardening temperature and cooling conditions be used for a series of steels, the relative depths of the hardened zones indicate the relative deep-hardenability of the steels of that series, eachto the others.

An object of this invention is to improve the deep-hardenability of hardenable steels generally, and of plain carbon and low alloy (less than 5% in the aggregate of elements other than iron and carbon) steels especially.

The deep-hardenability of steel may be enhanced in some degree by-adding in suitable percentages any one of the elements which can be taken into solid solution in steel at high temper atures, for instance, silicon, molybdenum, tungsten, chromium, or nickel. These hardening elements difi'er widely in the minimum percentage required to impart a useful degree of deep-hardenability, and in the maximum degree of deephardenability obtainable While maintaining other necessary properties of the steel.

I have found that beryllium may be used to impart an even further enhanced deep-hardenability to steels containing between 0.25% and 2% silicon, without substantially sacrificing other desirable properties of the steels. I have further observed that combination of beryllium with one or more of the further elements: the alkali metals, alkaline earth metals, aluminum, titanium, zirconium, uranium, cerium, thorium, vanadium, columbium, and tantalum, in percentages greater than those required for grain-refinement, considerably enhances the efiect of beryllium on deephardenability.

The present invention provides a beryllium steel in which beryllium is present in a percentage at least 0.0025% but less than 0.1%, and preferably between about 0.01% and 0.05%. The silicon content is between 0.25% and 2% and preferably between 0.35% and 1%. The carbon content is between 0.l% and 1%, and preferably between 0.2% and 0.8%. The minimum total proportion of said further element or elements to be added is any proportion greater than that required for grain-refinement, and preferably'up to several times that required for grain-refinement. The percentage required for optimum grain-refinement will depend to some extent on the kind of steel, the steel-making conditions, and the kind and number of deoxidizing and grainrefining elements used: but the total aggregate percentage of such further elements to be added will be between 0.03% and 1%, and a preferred range is between 0.05% and 0.3%.

In good steelmaking practice an addition of beryllium amounting to between 0.01% and 0.2% will yield residual berylliumin the final steel within the percentage limits specified above.

For eachelement and each combination of elements there appears to be an optimum percentage which imparts a maximum depth of hardenabllity and a frequent result of an increase in percentage'beyond the optimum is a decrease of deep hardenability below that imparted by the optimum, but for reasons of economy, or to obtain a steel having a certain desired combination of physical properties, it will often be desired to hardenabi'lity depths, in hundredths of an inch.

of steels containing about 0.50% carbon, 1.70% manganese, the indicated added percentages of other elements, and the remainder iron.

Composition, remainder iron Steel J omlny No. depth Si Mn Al 1 V I Zr 1 Be 1 Per Per Per Per Per Per cent cm! cent cent cent m1! Inch 0.27 1. 60 0. 04 0. 04 0. 04 None 0.21 0. 29 1.74 0. 04 0. 04 0.02 0.022 0. 33 0. 53 l. 75 0. 07 0. 07 0.07 None 0. 56 0. 49 1.65 0.09 0. 08 0. 04 0. 044 0.67 1. 0 1.07 0. 14 0. l4 0. 14 None 0.52 1.0 1.73 0.17 0.15 0.16 0. 015 0.63 1.0 1.65 0.18 0.18 0.09 0.088 0.74

1 Percentage added, all other rcentages determined by analysis. Residual beryllium between 20 a and 35% of percentage added.

Each of the steels in the table contains a total proportion of the elements aluminum, vanadium, and zirconium above that required for grain-o'eflnement. It will be observed that for a given silicon content those steels which contain a proportion of beryllium within the limits prescribed in this invention exhibit a marked increase in hardenability over steels containing no beryllium but of otherwise similar composition. In order to exhibit the remarkable eflicacy of beryllium additions even at the lower end of the specified range, a 1% silicon steel (steel No. 6) was treated with an addition of only 0.015% beryllium. In this steel the hardenabi'lity was greatly enhanced over a steel of similar composition containing no beryllium (steel No. The hardenability of this type of steel may be still further enhanced by a somewhat larger beryllium addition as is evidenced by the data on steel No. '7.

The eflicacy of beryllium additions in increasing hardenability is by no means limited to steels of the particular compositions shown in the table. These steels were selected only to demonstrate the practical application of the invention which is equally applicable to a wide variety of hardenable steels.

Beryllium may be introduced into the steel with a deoxidizing and grain-refining agent, for instance as an ingredient of complex deoxidizing agents containing 25% to silicon described in Patent 2,221,781, to J. H. Critchett and W. Crafts, or it may be separately introduced into the molten steel either before, during, or after the addition of the deoxidizing and grain-refining agent.

The advantages of the invention may be ex- I ploited in any of several ways. For instance, the cheaper steels among those described above may be used instead of more expensive, more highly alloyed steels heretofore used to obtain the desired strength. Or, present high strength steels may be even further strengthened by applying the principles of the invention, either by deeper hardening to a lower average hardness or by deeper hardening to the same or even higher hardness.

I claim:

1. A fine-grained steel quench-hardened article, other than a nitride case-hardened article, having substantially the composition: 0.25% to 2% silicon; manganese in a substantial proportion up to 2%; 0.1% to 1% carbon; between 0.0025% and 0.05% beryllium; 0.03% to 1% in the aggregate of at least one deoxidizing grainreflning element; remainder substantially all iron.

2. A fine-grained steel quench-hardened article, other than a nitride case-hardened article, having substantially the composition: 0.35% to 1% silicon; manganese in a substantial proportion up to 2%; 0.2% to 0.8% carbon; between 0.01% and 0.05% beryllium; 0.05% to 0.3% in the aggregate of at least one deoxidizing grainreflning element; remainder iron.

WALTER CRAFTS. 

